1. Field of the Invention
The present invention relates to an image receiving apparatus, and a control method, program, and recording medium for an image receiving apparatus, and in particular relates to techniques to be used when data is omitted in sending images over a network.
2. Description of the Related Art
In recent years, the Internet has become widely used, and information is frequently communicated via a network. Thus, various forms of information such as text, image, and audio can be exchanged, and moving images are also a type which can be exchanged via a network. Therefore, not only video recorded beforehand, but video taken in live coverage and for monitoring purposes can also be exchanged. As a result, demand for exchanging video, and immediately transmitting video taken in live coverage, or for monitoring, to the side receiving the information so as to reproduce the image, has been increasing.
Normally, communication protocols such as TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are used for Internet communication. TCP assures correct data transmission, so communication can be made with high reliability. However, a large transmission bandwidth is used to open a connection, and also erroneous data is subjected to a retransmission processing, so a delay may occur in the transmission of data.
On the other hand, UDP does not necessarily assure a highly reliable communication function, and error and omissions of the data may occur, thereby lowering reliability. However, since there is no need to open or close a connection, the transmission process can be performed at a high speed. A moving image is continuous data of a large size, so in the case of reproduction in real-time, transmitting at a high speed is necessary. Accordingly, in the case of transmitting a moving image with the Internet, UDP is often used because of its high transmission speed.
In the case of reproducing video data in the same time as the time that the video data is generated, erroneous data is retransmitted, whereby the video frame rate is lowered. Thus, for example, Japanese Patent Laid-Open No. 11-331839 discloses a video transmission/retransmission apparatus to perform data transmission without requiring retransmission of all data, and avoiding omission of important information. The video transmission/retransmission apparatus described in Japanese Patent Laid-Open No. 11-331839 computes the importance of data to be transmitted, based on (1) through (4) below, and performs a retransmission request for data with high importance.
(1) Positional information of which position on a screen the data will be displayed at time of reproduction.
(2) Degree of change within a frame which is one frame before the frame during transmission processing, of whether there is any change to the video data at the same position as the transmitting video data.
(3) Correlation of a scene of whether there is any change to the video scene of the entire frame by comparing the frame during transmission processing with one frame preceding.
(4) In the case that a transmitter reads multiple different video and transmits the video data, correlation of whether each video has great movement as a video, is relatively compared.
For example, in the case that an error location in a frame including an error is far away from the center of the frame, or the amount of change thereof is small in comparison with the preceding frame, this frame is not subject to a retransmission request. Also, in the case where the amount of change in a video scene of an entire frame is small, this frame is not subjected to a retransmission request.
However, the video transmission/retransmission apparatus described in Japanese Patent Laid-Open No. 11-331839 can only perform a retransmission request as an error handling process of an error frame. In addition, at the server side, an entire frame determined to have an error is transmitted in accordance with the retransmission request, so the processing load becomes large. Particularly, in the case that one server manages multiple clients, the processing load for retransmission data becomes extremely large. Therefore, the problem with the increase in traffic from retransmission has not been sufficiently prevented.
Thus, in order to prevent an increase in traffic from retransmission, the importance threshold is increased to reduce the frames subjected to retransmission request. However, the frames without a retransmission request cannot be handled, so there has been a problem in that omission of important information cannot be sufficiently avoided.